JPS62262745A - Catalyst carrier for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To enhance the high-temp. durability of a catalyst by incorporating alpha-alumina and theta-alumina in the coating layer on the upstream side of a base material, and incorporating alpha-alumina and gamma-alumina in the coating layer on the downstream side. CONSTITUTION:When a coating layer of activated alumina is laminated on the honeycomb monolithic base material, alpha-alumina and theta-alumina are incorporated in the coating layer of activated alumina on the upstream side in the flowing direction of exhaust gas. Furthermore, delta-alumina and gamma-alumina are incorporated in the coating layer of activated alumina on the downstream side, and the catalyst carrier for purifying exhaust gas is formed. Cordierite, mullite, etc., are used as the honeycomb monolithic base material, and triangular, square, and corrugated cell structures are appropriately used. Platinum, palladium, and rhodium are appropriately used as the metals to be deposited on the catalyst carrier.

Description

[Detailed description of the invention] [Industrial field of application] This invention is applicable to hydrocarbon (HC), carbon oxide (CO)
The present invention also relates to a catalyst carrier for use in detoxifying nitrogen oxides (NOx), and in particular to a catalyst carrier for use in purifying automobile exhaust gas and stationary engine exhaust gas.

[Prior art] Monolithic carriers (monolith carriers) are available in various materials, shapes, and manufacturing methods, but generally, cordierite and prismatic cell carriers manufactured by Corning and Nippon Insulators are used. Monolithic carriers are often used. Since this cordierite monolithic support has a very small specific surface area of about 1 m/11, even if a catalytic metal such as a noble metal is supported, it cannot be dispersed on the surface of the support. the result,
The catalyst obtained is poor in both initial performance and durability, and it is not practical to use it as a carrier as it is. Conventionally, in order to solve the above-mentioned drawbacks, an activated alumina coating was formed on the monolith carrier to increase the total specific surface area, improve the dispersibility of the catalyst metal, and improve performance. .

Conventionally, the activated alumina used for this alumina coating is
As seen in Special Publication No. 56-27295, about 50m
/! ! When alumina is used, the specific surface area is less than 50 m/I. α, θ
- There are few examples of active use of alumina. In JP-A No. 54-148187, θ-alumina is mixed in a part of the activated alumina, as seen in the description that δ-alumina is the main component, χ, γ, and θ, ρ-alumina are a part. There is a view that it is also good.

[Problem to be solved by the invention] Requirements for conventional catalysts for purifying automobile exhaust gas b).

The upper limit of the catalyst inlet gas temperature was around fsoo°C, indicating that it had thermal durability up to 800°C. However, in recent years, catalyst installation has been moved to the upstream part of the exhaust pipe and emphasis has been placed on use during high-speed driving, so the upper limit of the catalyst's artificial gas temperature has increased to around 900°C, and the catalyst temperature has increased to around 1000°C. It is thought that it has become a degree. As a result, high-temperature durability, which had not been given much importance in the past, has recently come to be viewed as a particular problem. Therefore, catalysts according to the prior art have insufficient high temperature durability.

To speculate on the reason for this, in the activated alumina species shown in Japanese Patent Publication No. 56-27295 and Japanese Patent Application Laid-open No. 54-148187, the crystals undergo transformation at a high temperature of 1000°C, and when new, the catalytic metal is Although it was supported in a highly dispersed manner, it is thought that sintering of the catalytic metal was promoted and the catalytic performance deteriorated.Additionally, when durability tests were conducted to investigate the durability of the catalyst, Deterioration in the performance of the catalyst in the upstream half of the exhaust gas flow path
It was found that the performance deterioration of the catalyst in half was greater than that of the Ib9. Furthermore, when the specific surface area of each catalyst was measured, the decrease in the specific surface area of the catalyst in the upstream half was significant, and it is thought that the cause of the performance deterioration was the high temperature condition that occurred in the upstream half.

Therefore, the problem with conventional catalysts is that they lack high-temperature durability, particularly in the upstream half.

[Means for Solving the Problems] The present inventors have conducted intensive research to solve the above-mentioned problems in the conventional technology, and as a result, they have developed an exhaust gas purifying catalyst that has superior high-temperature durability compared to conventional catalysts. Successfully provided a catalytic phase t* that can be obtained as follows.

That is, in the catalyst carrier for exhaust gas purification of the present invention, the activated alumina coating layer on the honeycomb monolith substrate for supporting catalyst metal has an activated alumina coating layer containing α-alumina and θ-alumina on the upstream side in the exhaust gas flow direction. It is characterized in that the downstream side is made of at least one kind selected from δ-alumina and γ-alumina.

In this invention, the monolithic carrier used as the base material is
Cordierite, mullite, etc. are used, and the base material preferably has a triangular, square, or wavy cell structure.

In addition, as the catalyst metal supported on the catalyst carrier of the present invention, it is preferable to use at least one of platinum, palladium, and rhodium.

[Function] The catalyst carrier of the present invention has an α-
Activated alumina including alumina and θ-alumina is applied as a coating layer, so that the catalytic metal supported thereon is not sintered by heat under high temperature conditions, resulting in high-temperature durability. can provide excellent catalysts.

In addition, the downstream side is less likely to reach high temperatures than the upstream side, and moreover, a-alumina and γ with a specific surface area of 50 m2/l or more
- Since it is coated with alumina, the dispersibility of the supported catalyst metal is good, and a catalyst with excellent durability can be provided.

[Example Example 1 Alumina sol manufactured by Nissho Kagaku Co., Ltd. (trade name As-200>70
0.9 (Alumina content 70! Rito, aluminum nitrate nonahydrate 601, ion exchange water 200#, specific surface area 1
Alumina which shows δ and r in X-ray diffraction at 00 m2/I/ is calcined at 1100'C for 3 hours to produce alumina powder (specific surface area shows 20 m2/l, and X-ray diffraction shows θ- and α- A slurry was prepared by mixing and stirring 1,000 g of alumina for 3 hours.

This slurry was designated as A slurry.

Next, as the alumina powder, alumina having a specific surface area of 100 m'/fl and showing δ and γ in Te A slurry was prepared by mixing and stirring, and this slurry was designated as Slurry B.

Cylindrical cordierite monolith carrier with 300 cells per square inch (manufactured by Nippon Insulator Co., Ltd., diameter 93+m, length 10100III, volume 0.6791)
f: The cell was immersed in water and taken out after sufficient water absorption, and the water remaining in the cell was blown away with an air flow (pressure of 5ki9/sub2). Half of this water-absorbed carrier (upstream part) is immersed in the previously prepared slurry A and taken out. Excess slurry in the cell adhering to the half of the carrier is removed from the opposite side to which no slurry is attached by air flow. I used it to blow it away. After drying the carrier to which slurry A was attached in this way at 110°C for 1 hour, it was fired in air at 700°C for 1 hour using an electric furnace.
A 431 A alumina coating was formed on the monolith carrier half (upstream portion).

In addition, only half of the monolithic carrier (the downstream part) on which the alumina coating is not formed is immersed in slurry B, and taken out. After drying the carrier at 110°C for 1 hour, it was heated to 700°C in the air using an electric furnace.
After firing for 1 hour, a 43.9 B alumina coating was formed on half of the monolith carrier (downstream part), and a total of 8611 A alumina coating was formed.
A catalyst carrier containing an alumina coating layer consisting of a film and a B film was obtained. When the alumina coating layer of this catalyst carrier was scraped off and the compound was identified and analyzed by X-ray diffraction, 0-alumina and α-alumina were detected from the upstream portion. Furthermore, from the downstream part, δ-alumina and r
-Alumina was detected.

Next, half of this catalyst carrier was immersed in a platinum ammine aqueous solution to adsorb the catalytic metal platinum onto the catalyst carrier, and then the remaining half was similarly adsorbed with platinum and further washed with water. Each half was immersed in a rhodium chloride aqueous solution to support the catalyst metal rhodium on the catalyst carrier, and then 1
After drying at 00°C, it was fired at 500°C for 30 minutes to obtain an exhaust gas purifying catalyst. Chemical analysis of the amount of precious metal supported on this catalyst revealed that the amount of platinum supported was 1.01/I
The supported amounts of t-catalyst and rhodium were 0.111/l-catalyst.

Example 2 As in Example 1, a coating film was formed using slurry A on the upstream portion of the monolithic carrier, and on the downstream portion as follows! A film was formed using the C slurry that had been split into one.

C slurry has a specific surface area of 130 as alumina powder.
This slurry was prepared by mixing and stirring a slurry having the same composition as the above-mentioned slurry, except that activated alumina showing γ-alumina in X-ray diffraction was used and ion-exchanged water 350Jii was used. When the alumina coating layer of this catalyst carrier was scraped off and the identification analysis of the silica compound was performed using X-ray diffraction, it was found that θ- and α-alumina,
Also, r-alumina was detected from the downstream part.

Next, as in Example 1, one portion of platinum was added to this coated carrier.
．． 011/l-catalyst and rhodium at 0.1 g/l-
A catalyst-supported catalyst for exhaust gas purification was obtained.

Example 3 Similarly to Example 1, a coating film was formed on the upstream part of the monolithic carrier using slurry A, and a coating film was formed on the downstream part using slurry D prepared as follows. .

D slurry has a specific surface area of 50 m as alumina powder.
2/I, using activated alumina that shows δ- and θ-alumina in X-ray diffraction, and using 300% ion-exchanged water. This slurry was prepared by mixing and stirring a slurry having the same composition as the above-mentioned slurry except that F was used.

Scrape off the alumina coating layer of this catalyst carrier,
Identification by X-ray diffraction reveals θ- and α-alumina from the upstream portion, and δ-alumina from the downstream 1111 portion.
and θ-alumina were detected.

Next, as in Example 1, 11/l of platinum was added to this catalyst carrier.
- supporting m medium and rhodium 0.111/l-catalyst,
A catalyst for exhaust gas purification was obtained.

Comparative Example 1 Slurry A used in Examples 1, 2, and 3 was coated on the entire monolithic carrier, dried, and fired to form a film of 86 g. Scrape off this coating layer and
When identified by line diffraction, α and θ alumina were detected. As in Example 1, 1.0% platinum was added to this coated carrier.
A catalyst for exhaust gas purification was obtained by supporting a Vl-catalyst and rhodium in an amount of 19/l-catalyst.

Comparative Example 2 The entire monolithic carrier was coated with the B slurry used in Example 1, dried and fired to form a coating of 861. When this coating layer was scraped off and identified by X@ diffraction, δ and γ alumina were detected. A 1.01/l platinum catalyst and a 0.1 g/l rhodium catalyst were supported on this coated carrier in the same manner as in Example 1 to obtain an exhaust gas purifying catalyst. Comparative Example 3 Used in Example 2 The entire monolithic support was coated with the C slurry, dried and fired to form a coating of 86 g. When this coating layer was scraped off and identified by X-ray diffraction, γ-alumina was detected. As in Example 1, 1.011/l of platinum and 0.11/l of rhodium were supported on the coated carrier to obtain an exhaust gas purifying catalyst. First, Examples 1 to 3 and Comparative Example 1
-3 forms of alumina are shown together.

Table 1 Example 4 and Comparative Example 4 Platinum ammine aqueous solution and palladium chloride aqueous solution 0.51/
An exhaust gas purifying catalyst was obtained by supporting an It-catalyst and a rhodium 0.111/l-catalyst.

Example 5 and Comparative Example 5 /4'radium 1.01 was added to the catalyst carrier obtained in Example 1 and Comparative Example 1 in the same manner as in Example 1 using an aqueous palladium chloride solution and an aqueous rhodium chloride solution, respectively.
An exhaust gas purifying catalyst was obtained by supporting a /l-catalyst and a rhodium 0.11/l-catalyst.

Catalyst durability performance evaluation test results The durability test conditions were an engine with an exhaust gas of 1380 occ, a rotation speed of 3300 rpm, and a boost of -100 mHg.
The conditions were to expose the catalyst to exhaust gas for 50 hours at a catalyst gas temperature of 890°C and an air-fuel ratio of 14.5. In this way, the performance evaluation of the durable catalyst is
Exhaust gas is passed through a 600cc engine catalyst to convert hydrocarbons (
) IC), -carbon oxide (Co), g
1 was calculated using Futo 2. These results are shown in Table 2.

Table 2 [Effects of the Invention] As is clear from the above results, the catalyst carrier of the present invention is a catalyst with extremely superior high-temperature durability compared to the conventional catalyst carrier supporting the same catalyst metal. performance can be demonstrated.

Claims (1)

[Claims] In a catalyst carrier for exhaust gas purification made of a honeycomb monolith base material coated with activated alumina, the activated alumina coating layer on the upstream side in the direction of the exhaust gas flow path is made of activated alumina containing α-alumina and θ-alumina. 1. A catalyst carrier for exhaust gas purification, wherein the coating layer is a coating layer of activated alumina on the downstream side, and the coating layer is made of activated alumina containing at least one selected from δ-alumina and γ-alumina.